Since your blog was interested and I have NO life, here's all the figures I could pull up on WWE DVD sales numbers. These are for North America (possibly the United States) only.
Only THREE WWE DVDs have sold over 100,000 units at the Manufactures Suggested Retail Price. This does not factor in bundle sales, clearance, etc. It WOULD factor in store sales, such as Best Buy which always has the movies on sale the first week they are released.
The top three are...
#1: The Rise & Fall of ECW (aprox 165,000 units at MSRP)
#2: Hulk Hogan: The Ultimate Anthology (aprox 125,000 units at MSRP)
#3: The Ultimate Ric Flair Collection (aprox 110,000 units at MSRP)
That puts it in perspective of what the very top of the ladder is. I'm guessing wrestling fans thought these things sold millions. They don't. BUT understand that they're the WWE's most profitable division because all the stuff contained in them is just archival footage. It costs pennies on a dollar to produce these sets.
The average set sells around 25,000 units. Here are the ones that are above average performers. If a DVD released after 2008, I did a rough guess based on removing the overseas stuff using sales data from older stuff. And since you can take it with a grain of salt, I put a * next to any such set.
Bloodbath: Wrestling's Best Cage Matches (about 85,000 copies)
Tombstone: The History of the Undertaker (About 70,000 copies)
The Road Warriors (about 55,000 copies)
Bret Hart (about 45,000 copies)
Shawn Michaels: From the Vault (about 45,000 copies)
Greatest Stars of the 80s (About 35,000 copies)
Shawn Michaels: Heartbreak & Triumph (about 30,000 copies)*
John Cena: My Life (about 30,000)*
Chris Benoit: Hard Knocks (about 25,000 copies)
And these are the under performing ones...
Eddie Guerrero: Cheating Death, Stealing Life (about 20,000 copies)
ECW Blood Sport (about 17,500 copies)
Rey Mysterio: The Biggest Little Man (about 15,000 copies)*
Mr. Perfect (about 7,500 copies)
History of the AWA (about 5,000 copies)
Roddy Piper (about 3,000 copies)
Dusty Rhodes (about 2,500 copies)
History of WCCW (about 2,500 copies)*
ECW Extreme Rules (about 2,000 copies)*
Brian Pillman (about 1,500 copies)
Superstar Billy Graham (about 1,000 copies)
I tried to get numbers for the 2009 releases but they were all over the place. More then likely places reporting them made the numbers up based on how much they liked the sets. The WWE the actual numbers pretty well guarded. I was told that Kane's release was the lowest single-wrestler set of the last year (released in December of 2008 but they factor it into the last calendar year).
I think actually the WWE likely has readjusted their expectations for what a DVD is expected to sell. And mind you, in the music industry a concert DVD that says 5,000 units is considered to be a MAJOR success. So the WWE isn't exactly hurting from this drop in sales. This is all stuff that is 'in the can'.
Sources: Billboard, Video Shop Magazine, WWE's pre-2008 sales figures.